Does this exist? I ran into a problem with vignetting on one of my lenses. I tried to add a rubber hood, step-up ring, and filter, but it's too much even with a high-quality, slim filter. Is there such a thing as a lens hood that incorporates a step-up ring into its threads? I've searched these forums, shopping sites, and general internet searches, but haven't found anything.

Not really sure what you're trying to do. Hoods with threads? Normal hoods don't have anything to do with the filter threads. Its also not clear how you're wanting to assemble things. What is attached to what in what order?

My best guess is the generic rubber hood is the cause of the vignetting. Get a hood matched to your lens instead.

While some manufacturers make hoods meant for specific lenses, these often get in the way of step-up rings, restricting your use of filters on lenses with non-standard thread sizes.

Generic rubber hoods attach via the filter thread, and just like most filters, provide threads on the outside for further filter attachments. Their collapsible nature means you can easily access these threads for adding/removing filters. It also means I know the hood isn't causing vignetting, because the vignette is still there even when the hood is collapsed. It's just an issue of too many pieces (hood, step-up ring, and filter) on the end of a moderate wide-angle lens. But if the hood and step-up ring were one piece instead of two, the vignette might not be there.